The present invention relates to a method for determining and compensating a transmission function of a measurement apparatus, for example a spectrum analyzer or a vector analyzer.
Prior art methods of this type are disclosed in Hewlett Packard Journal, December 1993, p. 31 ff. or p. 47 ff. For the evaluation, the characteristic of the modulation signal used at the input side, and its exact time relation to the calibration signal, must be known. In many applications, this precondition is not given, for example when such a method is to be used in a measurement apparatus in which a single frequency calibration oscillator and an arbitrary sweep oscillator that increases linearly with frequency are indeed already present, as is the case for example in a spectrum analyzer. Since, however, particularly in such electronic measurement apparatuses with band-limiting filters, amplifiers or frequency-converting mixers, the frequency response of the measurement apparatus is influenced by these modules, (thus introducing a certain error to the measurement result), the determination of the transmission function is of particular importance in such measurement apparatuses. This is because when the amplitude and phase frequency response of the measurement apparatus are known, this apparatus can easily be compensated by a digital evaluation unit, thereby increasing measurement precision.